1. Field of the Invention
The present invention relates to a heat transmission tube, and more specifically to that built in an evaporator of a freezer, a coolant being boiled at the outer surface of which when the tube is used.
2. Description of the Related Art
The heat transmission tube disclosed in Published Unexamined Japanese Patent Application (PUJPA) No. 57-131992 (Japanese Patent Application No. 56-211772) can be named as a typical conventional tube which boils coolant brought into contact with the outer surface thereof through exchange of heat between the coolant and fluid in the tube, so as to enhance transmission of heat propagated on to coolant (to be called boiling heat transmission hereinafter). Such a heat transmission tube is characterized by having a first and second groove portion formed on the outer surface of the low-fin tube by a roll forming process. This type of heat transmission tube is used in a liquid or gaseous coolant. This tube exhibits a good property in terms of heat transmission rate since, in the tube, bubbles remaining in the groove make boiling continue, thereby increasing the amount of heat transmission. Thus, a high transmissibility can be achieved.
However, such a tube has a disadvantage of very poor boiling heat transmission in a case of low heat flux. In consideration of this problem, there has been a great proposal for a heat transmission tube which exhibits a high heat transmissibility in a low heat flux case, which leads to efficient use of a heat source of a low temperature.
In the meantime, a device in which the heat transmission tube is built, is used with various loads in accordance with necessity; therefore it is required that the tube exhibit a high and stable transmissibility not only in a high heat flux case but also in a low one.